A Systems-Thinking Approach to Transportation

Serendipity led Northwestern Engineering’s Marco Nie into transportation research.

Purpose, however, has fueled his ongoing commitment to the deeply interdisciplinary field, which holds far-reaching impacts on individuals and communities around the globe as well as the environment.

After earning an undergraduate degree in structural engineering in his native China, Nie began pursuing graduate work at National University of Singapore. The university rather hastily assigned Nie an adviser, a gifted storyteller who regaled Nie with stories of his transportation research. Nie quickly became fascinated by a large, complex system blending humans, infrastructure, and technology as well as societal values and political systems.

“I was hooked, and knew transportation was what I wanted to study,” said Nie, a professor of civil and environmental engineering whose research aims to drive policy and strategies capable of making transportation systems more efficient, sustainable, and equitable.

Since Nie’s 2006 arrival at Northwestern, the transportation sector has witnessed monumental changes ranging from electric vehicles to ridesharing to big data. Nie, meanwhile, has sharpened his research and the tools he uses to better understand and predict the behavior of transportation systems, including leveraging mathematical models and machine learning.

Most notably, though, Nie began incorporating value judgements into his work, inspired by The Theory of Moral Sentiments by Adam Smith as well as A Theory of Justice by John Rawls. Shunning the idea that value judgements are for philosophers, not engineers, Nie believes value judgments are baked into any design of engineering systems.

“Whenever we try to optimize something, we define an objective and that objective inevitably embeds some kind of value judgment, right?” Nie said, adding that engineers – or modelers, the term he prefers for himself – should be explicit about the values they inject into systems design.

Working alongside economists, computer scientists, sociologists, operations researchers, and urban planners, Nie investigates equity aspects of transit services, both traditional systems like buses and trains as well as emerging mobility options like ridesharing and e-scooters. And increasingly, Nie has tried to incorporate equity-centric values into transit design.

In one recent paper, for instance, Nie used a stylized transit design model incorporating various finance and operational decisions to examine fare-free transit through the lens of distributive justice. His analysis highlights the prices societies pay for their “value” and details sensible compromises addressing varied interests and ideologies.

Transportation doesn’t have a fixed set of solutions. It’s one-third art, one-third science, and one-third politics, so completely multidisciplinary. That provides a lot of flexibility and opportunity to think very broadly across different fields and find worthy solutions. Marco Nie

In a separate ongoing project funded by the US National Science Foundation, Nie’s team is borrowing computational methods from machine learning to tackle the large-scale leader-follower congestion games, a layered battle between an authority – say, a taxing body or transit authority – and travelers, who are trying to make beneficial decisions for themselves with respect to factors like time and cost. His work in computational transportation science offers potential solutions to some of transportation’s most pressing problems, such as how a city might compel local travelers to swap their vehicles for mass transit.

“If we want to become more sustainable and meet our carbon emission obligations, our transportation systems need to gradually move away from auto dependency,” Nie said. “Yet, to do that, we need to make transit systems more affordable, more efficient, and generally better so that people will use them.”

For Nie, the unlikely marriage of optimization, operations research, and mathematics with social science fields like behavioral economics and sociology forces creativity and unlocks positive impact for humans and the environment.

“Transportation doesn’t have a fixed set of solutions. It’s one-third art, one-third science, and one-third politics, so completely multidisciplinary,” he said. “That provides a lot of flexibility and opportunity to think very broadly across different fields and find worthy solutions.”